1. Field of the Invention
The present invention relates to an air conditioning system for vehicles, and more particularly to an air conditioning system suitable for use in a work vehicle having a hydraulic circuit and a refrigerating circuit such as a mobile crane vehicle.
2. Description of the Prior Art
Generally in a work vehicle such as a mobile crane vehicle in which the cabin is rotatable through an angle of 360.degree., the cooling water for the engine circulating below the cabin cannot be introduced into the cabin. The cooling water cannot be used as a source of heat for the cabin. Heat pump type heating and air conditioning systems are known to be mounted on such vehicles (for example, Japanese Unexamined Patent Publication SHO 61-122462).
This heat pump type system has a hydraulic circuit A and a refrigerating circuit B, as shown in FIG. 11. Hydraulic circuit A comprises a hydraulic pump 11 for pumping up hydraulic oil stored in oil tank 10, hydraulic motor 12 is driven by the oil pumped by hydraulic pump 11. Radiator 13 radiates heat from the oil discharged from hydraulic motor 12. The hydraulic oil flows as shown by the broken line arrows in FIG. 11. The hydraulic oil drives hydraulic motor 12. Relief valve 14 controls the oil pressure introduced into hydraulic motor 12.
Refrigerating circuit B comprises: compressor 20; four-way valve 21; heat exchangers 22, 23 and 24; receiver 25; expansion valve 26; and check valves 27a, 27b, 27c and 27d. Compressor 20 is driven by the rotational force of hydraulic motor 12 provided in hydraulic circuit A. The first heat exchanger 22 is brought into thermal contact with radiator 13 of hydraulic circuit A. The second heat exchanger 23 is disposed in an air conditioning air duct 28 communicating with the inside of the cabin.
When heating is to be performed, a working fluid is circulated in the order of compressor 20, four-way valve 21, second heat exchanger 23, check valve 27a, receiver 25, expansion valve 26, first heat exchanger 22, check valve 27b, four-way valve 21 and compressor 20, as shown by the solid line arrows in FIG. 11. The inside of the cabin is heated by the radiating operation of the second heat exchanger 23.
When air conditioning (air cooling) is performed, the working fluid is circulated in the order of compressor 20, four way valve 21, third heat exchanger 24, check valve 27c, receiver 25, expansion valve 26, check valve 27d, second heat exchanger 23, four-way valve 21 and compressor 20, as shown by the broken line arrows in FIG. 11. The inside of the cabin is cooled by the endothermic operation of the second heat exchanger 23.
In such a conventional air conditioning system, however, although the system can satisfy the operations of air cooling in summer and heating in winter, respectively, the system cannot achieve dehumidification and heating required in, for example, the rainy season. Further, since the conventional air conditioning system is a heat pump type system, many parts are required for assembling the system, and the cost of the system is expensive.